This application is based on and claims priority to Japanese Patent Application numbers 11-320864, filed Nov. 11, 1999, and 2000-3385, filed Jan. 12, 2000.
1. Field of the Invention
The present invention generally relates to a vehicle suspension system for use in four-wheeled vehicles having two or more interrelated damper units. More particularly, the present invention to the sizing and configuration of certain components within such a vehicle suspension system so as to provide improved interrelationships between the components for controlling vehicle movement.
2. Description of the Related Art
Vehicle suspension systems have been proposed that embody individual hydraulic dampers associated with each of the wheels for damping their respective motion. As a further improvement upon this arrangement, systems have been proposed wherein pairs or more of wheels may be interrelated to control the roll and/or pitch of a vehicle in addition to individual wheel damping when encountering objects. For instance, during rapid deceleration or emergency braking, the suspension system allows interaction between the front and rear suspended members. Moreover, during cornering, the vehicle suspension system allows interrelation between the suspended members to increase traction and control. Various systems have been proposed for accomplishing these effects, many of which have become quite complicated in nature and in construction. Often involving electronic sensors and complicated control strategies.
One particular advantageous type of system and numerous embodiments of it is disclosed in U.S. Pat. No. 5,486,018, issued Jan. 23, 1996. In this type of system, each wheel is associated with a hydraulic damper that is comprised of a cylinder in which a piston reciprocates. The cylinder is connected to either the wheel or the vehicle body and the piston is connected by a piston rod to the remaining vehicle component. The piston divides the cylinder into a pair of fluid chambers one of which may be considered to be a working chamber and the other of which may be considered to be a reservoir chamber. A damp valve arrangement is provided for controlling the flow between the working cylinder portion and the reservoir chamber thus, the individual units act like conventional shock absorbers.
However, the piston rod displaces a volume in one of the chambers and thus, it is necessary to provide a reservoir where the displaced fluid may be added and subtracted to compensate for the piston rod displacement amount. In accordance with the embodiments disclosed in that patent, pairs of wheels have a common reservoir arrangement which acts as a pressure control system. The makeup fluid from each unit is transferred to a respective variable volume chamber and the movable elements of those two chambers are interlinked to each other so as to provide additional suspension control between the two associated wheels for controlling vehicle body movement. This can be utilized to reduce roll and/or pitching.
For example, if the associated or interconnected wheels are at opposite sides of the vehicle when both wheels strike an obstacle, each piston and cylinder of the shock absorbing unit will undergo the same movement in the same direction. The differential fluids are transferred between the pressure control device and will cause equal displacements of the movable members that are interrelated and the system operates as a conventional suspension system. If, however, the vehicle is maneuvered around a curved path of travel, one suspension unit (i.e., the one on the outside) will tend to be compressed while that on the inside will tend to expand. Thus, there is a differential flow of fluid between the units and the interconnection provides further damping control resistance of such body motion.
The difficulty with this type of system is that the requirements in terms of size and capacity of the individual shock absorbers differ for optimum damping depending upon whether the displacement occurs during normal straight-ahead movement or when rounding a curve. Similar situations are true with respect to front and rear interconnected suspensions for damping pitching movements during acceleration or braking. That is, when the pressure control device is acting to damping body movements between the two wheels, the pressure control device works in combination with the respective shock absorbers because of this the individual wheel shock absorbers should be somewhat smaller to reduce the effect on the overall body control. Thus, the individual shock absorber design tends to be a compromise between the optimum for these two different damping conditions.
With reference now to FIG. 1, a vehicle suspension system of the interrelated type is disclosed therein. The suspension system indicated generally by the reference numeral comprises two mirrored halves in the illustrated arrangement each halve comprises a first damper 22 and a second damper 24. In the illustrated arrangement, the first damper 22 and the second damper 24 are connected through a pressure regulator 26. As indicated by the phantom lines in FIG. 1, a single pressure regulator 26 can be interconnected to the first damper 22 (i.e., a front damper) and a second damper (i.e., a rear damper). In some arrangements, a cross-relationship may arise such that a front left damper is connected to a rear right damper and a front right damper is connected to a rear left damper. Such a construction is illustrated with phantom lines in FIG. 1. In other arrangements, a front left damper will be connected to a rear left damper while a front right damper will be connected to a rear right damper such as that illustrated in solid lines in FIG. 1.
In the illustrated arrangement of FIG. 1, the first damper 22 is configured of a cylinder 28 in which a piston 30 is arranged to reciprocate. A piston rod 32 connects to the piston 30 at one end and to a component of the vehicle at the other end. As is known, the damper 22 is positioned between a sprung and unsprung number of the vehicle. For instance, as is generally known in a sprung portion of the vehicle (i.e., the vehicle body) differs from the unsprung portion of the vehicle (i.e., the suspension), in that a spring is positioned between the vehicle body and the operating surface whereas the unsprung portion of the vehicle does not have a spring interposed between its and the operating surface. In the illustrated arrangement, the piston rod 32 is connected to one of the vehicle body and the wheel whereas the cylinder 28 is connected to the other of the two members. Such a construction advantageously results in an upper fluid chamber 34 and a lower fluid chamber 36 that are segregated from each other by the piston 30.
The piston 30 preferably has one or more passages 38 defined therethrough which allow communication between the upper fluid chamber 34 and the lower fluid chamber 36. As will be appreciated, the term upper and lower are relative and used for ease of description but need not be an upper and lower chamber in all instances. A throttle valve 40 preferably is disposed along the passage 38 to control the flow of fluid between the upper fluid chamber 34 and the lower fluid chamber 36. It should be noted that a similar construction is used for each of the dampers 22, 24 in the illustrated arrangement of FIG. 1. Accordingly, the components associated with each of these dampers 22, 24 will not be further described.
The upper and lower fluid chambers 34, 36 preferably are filled with a fluid or gas such as that known to those of ordinary skill in the art. As such, the first damper 22 and the second damper 24 are in fluid communication with one another through the pressure regulator 26. The pressure regulator 26 in the arrangement illustrated in FIG. 1, comprises a first cylinder 42 and a second cylinder 44. The first cylinder and the second cylinder 42, 44, generally are formed within a single outer body. The first cylinder 42 has a first oil chamber or fluid chamber 46 which is in direct communication with the upper fluid chamber 34 of the first damper 22. Similarly, the second cylinder 44 has a second fluid chamber 48 that is in direct fluid communication with the upper fluid chamber 34 of the second damper 24.
In the arrangement illustrated in FIG. 1, a high pressure gas chamber 50 is defined in a lower portion of the body 52. A piston 54 is interposed between the high pressure gas chamber 50 and the first cylinder and second cylinder 42, 44. Moreover, a single throttle valve 56 is interposed between the first fluid chamber 46 and the second fluid chamber 48. In addition, the piston 54 is sized and configured such that the first oil chamber 46 and the second oil chamber 48 have the same effective cross-sectional areas such that the same force will be exerted from both the first cylinder 42 and the second cylinder 44 upon the piston 54.
The arrangement described above produces a damping force through the valves 40 which are disposed within the pistons 30 of both the first damper 22 and the second damper 24 when the first damper 22 and the second damper 24 work in generally the same direction with approximately the same displacement. However, when the first damper 22 and the second damper 24 operate in opposite directions or with varying amounts then damping forces are also produced through the single valve 56 that is defined between a first cylinder 42 and the second cylinder 44. Thus, when the front wheels in the illustrated arrangement and the rear wheels encounter similar conditions causing vertical displacement in the same direction of approximately the same amount, the only damping forces created are through the valves 40. However, when the front dampers and the rear dampers act in opposite directions, such as during emergency braking for instance, then an additional damping force is provided by flow which will occur through the valve 56. Accordingly, the damping forces are greater in the illustrated arrangement during panic stops and rapid accelerations as compared to vehicle turning.
As discussed above, in some arrangements, there may be a cross-configuration between the front left cylinder or damper 22 and the rear right damper 24. In such cross-interrelations, similar phenomena can be expected, however, under this construction, the damping forces will tend to be higher when the vehicle rolls or pitches than when the vehicle bounces.
Unfortunately, in the above-described suspension system, close tolerances as well as dimensions must be maintained among each of the four cylinders or dampers. In addition, close dimensional parity must be maintained between the two pressure regulators as well as the lever ratios of the suspension system. As is known to those of ordinary skill in the art, a lever ratio varies depending upon the mounting angle and location of the various suspension components. For instance, if a damper were to be mounted vertically atop of an axle, it would be said to have a one-to-one lever ratio i.e., one inch of vertical shock travel would be the same as one inch of vertical wheel travel. If, however, the shock was mounted at a 45xc2x0 angle, it will move approximately one-half the amount that the wheel moves, i.e., one-half inch of vertical shock travel for one inch of vertical wheel travel. As such, it would be said to have a 1.5 to 1 lever ratio.
Due to the restrictions on the configuration and sizing of the components, arranging a suspension system for both the front and rear wheels to adapt to weight distribution changes becomes fairly difficult in addition, the restrictions placed on the design of the suspension system reduces the degrees of freedom available when designing the front and rear suspension systems.
Such difficulties can be lessened to some extent by mutually changing the configuration of both the front and the rear suspension systems. However, in order to change the configurations, the ultimate result must be designed such that the damping forces produced by the throttle valves do not differ regardless of whether the front cylinders or dampers are being compressed and the rear dampers are being extended or whether the front dampers are being extended while the rear dampers are being compressed.
Accordingly, one aspect of the present invention involves a vehicle suspension system comprising a first damper and a second damper. The first damper and the second damper are interrelated. The first damper comprises a first piston and a first cylinder body. A first cylinder bore is defined by the first cylinder body. The first piston is arranged to reciprocate within the first cylinder bore. The first piston has a first effective area a1. The first damper extends between a first wheel and a vehicle body. The second damper comprises a second piston and a second cylinder body. A second cylinder bore is defined by the second cylinder body. The second piston is arranged to reciprocate within the second cylinder bore. The second piston has a second effective area a2. The second damper extends between a second wheel and the vehicle body. A first chamber is defined within the first cylinder body at least in part by the first piston. A second chamber is defined within the second cylinder body at least in part by the second piston. A first pressure regulating cylinder is in fluid communication with the first chamber and a second pressure regulating cylinder is in fluid communication with the second chamber. The first pressure regulating cylinder comprises a first variable volume chamber and the second pressure regulating cylinder comprises a second variable volume chamber. The first variable volume chamber and the second variable volume chamber are defined at least in part by a single moveable member. The single moveable member has a first subarea A1 that corresponds to the first variable volume chamber and a second subarea A2 that corresponds to the second variable volume chamber. A bypass passage extends between the first variable volume chamber and the second variable volume chamber and a first throttle valve and a second throttle valve are positioned within the bypass passage.
Another aspect of the present invention involves a vehicle suspension system comprising a first damper and a second damper. The first damper and the second damper are interrelated. The first damper comprises a first piston and a first cylinder body. A first cylinder bore is defined by the first cylinder body. The first piston is arranged to reciprocate within the first cylinder bore. The first damper extends between a first wheel and a vehicle body. The second damper comprises a second piston and a second cylinder body. A second cylinder bore is defined by the second cylinder body. The second piston is arranged to reciprocate within the second cylinder bore. The second damper extends between a second wheel and the vehicle body. A first chamber is defined within the first cylinder body at least in part by the first piston. A second chamber is defined within the second cylinder body at least in part by the second piston. A first pressure regulating cylinder is in fluid communication with the first chamber and a second pressure regulating cylinder is in fluid communication with the second chamber. The first pressure regulating cylinder comprises a first variable volume chamber and the second pressure regulating cylinder comprises a second variable volume chamber. The first variable volume chamber and the second variable volume chamber are defined at least in part by a single moveable member. A bypass passage extends between the first variable volume chamber and the second variable volume chamber and a first throttle valve and a second throttle valve are positioned within the bypass passage. Means for substantially stopping flow through the bypass passage when the first wheel and the second wheel move relative to the vehicle body also are provided.